The continuing evolution of microprocessor control has enabled more comprehensive and complex vehicle control strategies. As is well known, an electronic control unit (ECU) utilizing a microprocessor is often employed to control a variety of functions for all types of vehicles, including heavy-duty tractor-semitrailer trucks. The ECU receives inputs from strategically located sensors indicating various vehicle operating parameters. This information is then processed by a predetermined set of instructions which also determines which outputs to energize to effect control of the vehicle.
The accuracy of any control system, including vehicle control systems, depends on a number of variables including the thoroughness and accuracy of the information obtained from the input sensors. Of course, the ECU can effect more sophisticated control if provided with more accurate and complete data. However, the economic considerations imposed by large-scale manufacturing of vehicles, limits the number of sensors and the accuracy of the sensors utilized in such applications.
Therefore, it is desirable to combine data obtained from various existing sensors and use that data to approximate other vehicle parameters which are difficult to measure directly or not critical to vehicle control, thereby eliminating the need for an additional sensor. One parameter which is difficult to economically measure directly, but used in controlling commercial vehicles such as heavy-duty tractor semitrailer trucks, is the vehicle mass. More precisely, the current vehicle mass relative to a prior vehicle mass. The mass of a vehicle such as a tractor-semitrailer truck may vary significantly depending upon whether the trailer is loaded, unloaded, or disconnected from the tractor.
The relative vehicle mass is an important parameter which may be used in vehicle control, especially for control of vehicle braking in tractor-semitrailer trucks. Braking systems for such vehicles are difficult to design since the load, which often varies substantially, affects braking performance. For example, the braking system must effectively operate when the vehicle is a tractor only, a tractor with an empty or lightly loaded trailer, or a tractor with a heavily loaded trailer. Thus, the relative vehicle mass is one of several vehicle operating parameters which may be used to select an appropriate braking mode of operation, such as work balance, proportioning, or ABS.
It would therefore be desirable to provide a method and system for determining relative vehicle mass. Once the relative vehicle mass is known, a particular braking mode can be selected so that the ECU can control the applied braking force delivered to each of the vehicle braking sites based on the known relative vehicle mass. Thus, it is unnecessary for the vehicle operator to compensate for a larger vehicle mass by applying greater pressure to the brake pedal, since the vehicle braking control system will automatically adjust the delivered braking force for the current vehicle loading condition. As a result, more precise braking is effected.